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The barn swallow (Hirundo rustica) poses a number of fascinating scientific questions, including the taxonomic status of postulated subspecies. Here, we obtained and assessed the sequence variation of 411 complete mitogenomes, mainly from the European H. r. rustica, but other subspecies as well. In almost every case, we observed subspecies-specific haplogroups, which we employed together with estimated radiation times to postulate a model for the geographical and temporal worldwide spread of the species. The female barn swallow carrying the Hirundo rustica ancestral mitogenome left Africa (or its vicinity) around 280 thousand years ago (kya), and her descendants expanded first into Eurasia and then, at least 51 kya, into the Americas, from where a relatively recent (

The 2010 Deepwater Horizon (DWH) disaster led to extensive oil deposition in Louisiana’s coastal wetlands, followed two years later by Hurricane Isaac. These disturbances led to changes in saltmarsh invertebrate communities, potentially affecting higher-level predators and the saltmarsh food web. Seaside Sparrows (Ammospiza maritima) are ubiquitous, year-round residents of the coastal saltmarsh affected by the DWH spill, where they consume diverse invertebrates and may be considered an indicator species for the ecosystem’s integrity. We used DNA metabarcoding to evaluate prey consumed by Seaside Sparrows to understand how sparrows responded to residual contamination from the DWH oil spill and ecosystem disturbance caused by Hurricane Isaac. To do so, we evaluated metrics of diet (prey richness, diversity, overall diet composition) and resource use (total niche width, individual specialization) from 2011 to 2017 on oiled, unoiled, and reference sites. We found that while diet composition varied across years and site type, Hurricane Isaac had an even greater effect on the richness and diversity of prey consumed. Resource use—as measured by the total niche width of the populations and degree of individual specialization—was most stable on unoiled sites compared to unoiled and reference sites. Finally, we analyzed resource use for each combination of site type and year (i.e.: “2014 oiled sites”), which indicated a strong correlation between individual specialization and total niche width: as total niche width increased, individuals became more specialized, following the predictions of the Niche Variation Hypothesis.

Insights into the evolution of non-model organisms are often limited by the lack of reference genomes. As part of the Vertebrate Genomes Project, we present a new reference genome and a pangenome produced with High-Fidelity long reads for the barn swallow Hirundo rustica. We then generated a reference-free multialignment with other bird genomes to identify genes under selection. Conservation analyses pointed at genes enriched for transcriptional regulation and neurodevelopment. The most conserved gene is CAMK2N2, with a potential role in fear memory formation. In addition, using all publicly available data, we generated a comprehensive catalogue of genetic markers. Genome-wide linkage disequilibrium scans identified potential selection signatures at multiple loci. The top candidate region comprises several genes and includes BDNF, a gene involved in stress response, fear memory formation, and tameness. We propose that the strict association with humans in this species is linked with the evolution of pathways typically under selection in domesticated taxa.

The objective of this paper is to present the results of discussions at a workshop held as part of the International Congress of Radiation Research (Environmental Health stream) in Manchester UK, 2019. The main objective of the workshop was to provide a platform for radioecologists to engage with radiobiologists to address major questions around developing an Ecosystem approach in radioecology and radiation protection of the environment. The aim was to establish a critical framework to guide research that would permit integration of a pan-ecosystem approach into radiation protection guidelines and regulation for the environment. The conclusions were that the interaction between radioecologists and radiobiologists is useful in particular in addressing field versus laboratory issues where there are issues and challenges in designing good field experiments and a need to cross validate field data against laboratory data and vice versa. Other main conclusions were that there is a need to appreciate wider issues in ecology to design good approaches for an ecosystems approach in radioecology and that with the capture of 'Big Data', novel tools such as machine learning can now be applied to help with the complex issues involved in developing an ecosystem approach.

In Chernobyl, chronic exposure to radioactive contaminants has a variety of deleterious effects on exposed organisms, including genetic damage and mutation accumulation. However, the potential for such effects to be transmitted to the next generation is poorly understood. We captured lesser marsh grasshoppers (Chorthippus albomarginatus) in the Chernobyl Exclusion Zone from sites varying in levels of environmental radiation by more than three orders of magnitude. We then raised their offspring in a common garden experiment in order to assess the effects of parental exposure to radiation on offspring development and DNA damage. Offspring that reached maturity at a younger age had higher levels of DNA damage. Contrary to our hypothesis, parental exposure to radioactive contamination did not affect DNA damage in their offspring possibly because of intervening adaptation or parental compensatory mechanisms. Our results suggest a trade-off between developmental rate and resistance to DNA damage, whereby offspring developing at faster rates do so at the cost of damaging their DNA. This result is consistent with and extends findings in other species, suggesting that faster growth rates cause increased oxidative damage and stress. We propose that growth rates are subject to stabilizing selection balancing the benefits of fast development and the competing need of buffering its damaging effects to macromolecules and tissues.

In 2010, the Deepwater Horizon oil spill released an estimated 4.9 million barrels of oil into the Gulf of Mexico, damaging coastal ecosystems. Seaside Sparrows (Ammospiza maritima)—a year-round resident of Gulf Coast salt marshes—were exposed to oil, as shown by published isotopic and molecular analyses, but fitness consequences have not been clarified. We monitored nests around two bays in Plaquemines Parish, Louisiana, USA from 2012–2017 to assess possible impacts on the nesting biology of Seaside Sparrows. A majority of nests failed (76% of known-fate nests, N = 252 nests, 3521 exposure-days) during our study, and predation was the main cause of nest failure (~91% of failed nests). Logistic exposure analysis revealed that daily nest survival rate: (1) was greater at nests with denser vegetation at nest height, (2) was higher in the more sheltered bay we studied, (3) decreased over the course of the breeding season in each year, and (4) was not correlated with either sediment polycyclic aromatic hydrocarbon concentrations or estimated predator abundance during the years for which we had those data. Although the Deepwater Horizon spill impacted other aspects of Seaside Sparrow ecology, we found no definitive effect of initial oiling or oiled sediment on nest survival during 2012–2017. Because predation was the overwhelming cause of nest failure in our study, additional work on these communities is needed to fully understand demographic and ecological impacts of storms, oil spills, other pollutants, and sea-level rise on Seaside Sparrows and their predators.

In marine species, the transcriptomic response to Deepwater Horizon (DWH) oil implicated many biochemical pathways, with corresponding adverse outcomes on organ development and physiological performance. Terrestrial organisms differ in their mechanisms of exposure to polycyclic aromatic hydrocarbons (PAHs) and their physiological challenges, and may reveal either distinct effects of oil on biochemical pathways or the generality of the responses to oil shown in marine species. Using a cross-species hybridization microarray approach, we investigated the transcriptomic response in the liver of Seaside Sparrows (Ammospiza maritima) exposed to DWH oil compared with birds from a control site. Our analysis identified 295 genes differentially expressed between birds exposed to oil and controls. Gene ontology (GO) and canonical pathway analysis suggested that the identified genes were involved in a coordinated response that promoted hepatocellular proliferation and liver regeneration while inhibiting apoptosis, necrosis, and liver steatosis. Exposure to oil also altered the expression of genes regulating energy homeostasis, including carbohydrate metabolism and gluconeogenesis, and the biosynthesis, transport and metabolism of lipids. These results provide a molecular mechanism for the long-standing observation of hepatic hypertrophy and altered lipid biosynthesis and transport in birds exposed to crude oil. Several of the activated pathways and pathological outcomes shown here overlap with the ones altered in fish species upon exposure to oil. Overall, our study shows that the path of oil contamination from the marine system into salt marshes can lead to similar responses in terrestrial birds to those described in marine organisms, suggesting similar adverse outcomes and shared machinery for detoxification.

Background The barn swallow (Hirundo rustica) is a migratory bird that has been the focus of a large number of ecological, behavioral, and genetic studies. To facilitate further population genetics and genomic studies, we present a reference genome assembly for the European subspecies (H. r. rustica). Findings As part of the Genome10K effort on generating high-quality vertebrate genomes (Vertebrate Genomes Project), we have assembled a highly contiguous genome assembly using single molecule real-time (SMRT) DNA sequencing and several Bionano optical map technologies. We compared and integrated optical maps derived from both the Nick, Label, Repair, and Stain technology and from the Direct Label and Stain (DLS) technology. As proposed by Bionano, DLS more than doubled the scaffold N50 with respect to the nickase. The dual enzyme hybrid scaffold led to a further marginal increase in scaffold N50 and an overall increase of confidence in the scaffolds. After removal of haplotigs, the final assembly is approximately 1.21 Gbp in size, with a scaffold N50 value of more than 25.95 Mbp. Conclusions This high-quality genome assembly represents a valuable resource for future studies of population genetics and genomics in the barn swallow and for studies concerning the evolution of avian genomes. It also represents one of the very first genomes assembled by combining SMRT long-read sequencing with the new Bionano DLS technology for scaffolding. The quality of this assembly demonstrates the potential of this methodology to substantially increase the contiguity of genome assemblies.

Studies of avian species have shown that maternal effects mediated by the transfer of egg hormones can profoundly affect offspring phenotype and fitness. We previously demonstrated that the injection of a physiological amount of testosterone (T) in the eggs of ring-necked pheasants (Phasianus colchicus) disrupted the covariation among male morphological traits at sexual maturity and positively affected male mating success. Here, we investigate whether egg T exposure affected adult male circulating T levels at the onset of the breeding season (reflecting gonadal maturation), and the relationship between circulating T and male traits. Egg T exposure did not affect pre-mating plasma T. T levels were not associated with the expression of secondary sexual and non-sexual traits or socio-sexual behaviour (social rank, overall fighting ability and mating success). However, wattle brightness decreased with increasing circulating T in males hatched from T-eggs (T-males) but not among control males. In dyadic encounters during the peak mating period, control males with higher premating T levels had higher chances of being dominant over other control males. However, higher pre-mating T levels did not predict success in male-male competition in encounters involving T-males. We suggest that the long-term effects of egg T on male phenotype do not originate from differential gonadal maturation according to egg T treatment. Rather, prenatal androgens may have priming effects on functioning of target tissues, translating into differential phenotypic effects according to androgen exposure during embryonic development.

Parents are expected to invest more in the sex that benefits most from the local environment. When the quality of breeding sites varies spatially and natal dispersal of males and females differs, parents in high-quality habitats should skew their progeny sex ratio in favor of the less dispersing sex. We tested this prediction in the barn swallow (Hirundo rustica L.), by relating the proportion of male offspring around fledging (secondary sex ratio) of first and second broods to the ecological quality (presence of livestock farming and relative surface of hayfields in the foraging range) and local demographic trends of the farms where the colonies were located. Consistent with our predictions, the proportion of male offspring, which are more philopatric than females, increased with the extent of hayfields, which are high quality, preferred foraging habitats. Moreover, the proportion of male offspring in second broods was smaller in colonies with positive demographic trends, possibly indicating density-dependent effects on sex ratio. Independent of the mechanism generating uneven sex ratio (zygote sex ratio adjustment or sex-related pre-fledging mortality), barn swallows breeding under favorable conditions overproduced the sex that is more likely to benefit from such conditions.

Evidence is accumulating that sex steroids in the eggs, besides affecting progeny phenotype and behavior in the short term, also have enduring effects until adulthood, when they may translate into differences in reproductive strategies and success. Maternal steroids transfer may therefore affect both agonistic behavior and mate choice decisions, either through the promotion of body size and condition or through a priming effect on the neuroendocrine system. However, owing to the prevalence of a short-term perspective, relevance of maternal transfer of sex steroids to sexual selection processes has been seldom studied. Here we investigate the effects of an experimental increase in egg testosterone on male dominance and copulation success in the ring-necked pheasant, Phasianus colchicus, a polygynous galliform with multiple male ornamental traits, in captivity. We found that females from testosterone (T) injected eggs copulated less than control females. Males from T-injected eggs obtained more copulations than control males, specifically with control females. The effect of male 'ordinary' and secondary sexual traits on either dominance or copulation frequency did not depend on early exposure to T, nor did T treatment affect male dominance. Present results demonstrate that variation in the early hormonal environment set up by mothers affects sexual behavior of the offspring, which might translate into fitness differences.

1.Ionizing radiation produces oxidative stress, but organisms can adapt to their exposure with physiological adaptive responses. However, the role of radioadaptive responses in wild populations remains poorly known. 2.At Chernobyl, studies of birds and other taxa including humans show that chronic exposure to radiation depletes antioxidants and increases oxidative damage. Here, we present analyses of levels of the most important intracellular antioxidant (i.e. glutathione, GSH), its redox status, DNA damage and body condition in 16 species of birds exposed to radiation at Chernobyl. We use an approach that allows considering the individual bird as the sampling unit while controlling for phylogenetic effects, thus increasing the statistical power by avoiding the use of species means as done for most previous comparative studies. 3.As a consequence, we found a pattern radically different from previous studies in wild populations, showing that GSH levels and body condition increased, and oxidative stress and DNA damage decreased, with increasing background radiation. Thus, when several species are considered, the overall pattern indicates that birds are not negatively affected by chronic exposure to radiation and may even obtain beneficial hormetic effects following an adaptive response. Analysis of the phylogenetic signal supports the existence of adaptation in the studied traits, particularly in GSH levels and DNA damage. 4.We also show that, under equal levels of radiation, the birds that produce larger amounts of the pigment pheomelanin and lower amounts of eumelanin pay a cost in terms of decreased GSH levels, increased oxidative stress and DNA damage, and poorer body condition. Radiation, however, diminished another potential cost of pheomelanin, namely its tendency to produce free radicals when exposed to radiation, because it induced a change towards the production of less pro-oxidant forms of pheomelanin with higher benzothiazole-to-benzothiazine ratios, which may have facilitated the acclimation of birds to radiation exposure. 5.Our findings represent the first evidence of adaptation to ionizing radiation in wild animals, and confirm that pheomelanin synthesis represents an evolutionary constraint under stressful environmental conditions because it requires GSH consumption

Random and subtle deviations from bilateral symmetry (fluctuating asymmetry) have long been of interest to biologists who wish to study the susceptibility of organisms to changes in environmental quality. However, the reliability of FA as a biomarker has come under question due to inconsistent results in the literature. We conducted a meta-analysis of published literature to test the hypothesis that FA is a reliable biomarker of environmental stress in insects and identify possible sources of variation amongst studies. We expected studies to detect larger, positive magnitudes of effect on FA in lab populations due to the lack of confounding effects from other environmental factors compared to wild populations. Additionally, we predicted that studies that used geometric morphometric approaches to FA in shape and size would be more sensitive to changes in environmental quality compared to linear and meristic measures and thus show larger effects on FA. We also expected anthropogenic stressors to generate significantly larger effects on FA compared to naturally occurring stressors due to the organisms’ inability to buffer developmental pathways against a novel stressor. Finally, we predicted comparatively larger magnitudes of effect in studies that verified the environmental factor acting on the organism was a stressor by detecting negative effects on fitness-related traits. Overall, we found that FA is a sensitive biomarker of environmental stress. Environmental stressors explained 36% of the variation of effect on FA across studies. Studies that demonstrated a negative effect of the stressor on fitness-related traits showed significantly larger, positive magnitudes of effect on FA compared to studies that did not detect an effect from the environmental stressor. Additionally, studies conducted under laboratory conditions detected significantly larger, effects on FA compared to field-based studies. The kind of trait measured and the novelty of the stressor did not significantly account for differences amongst studies. Thus, the use of FA as a biomarker of environmental stress is a legitimate tool particularly when studies verify the biological relevance of stressors for the study organism.

Tree growth has been hypothesized to provide a reliable indicator of the state of the external environment. Elevated levels of background ionizing radiation may impair growth trajectories of trees by reducing the annual growth. Such effects of radiation may depend on the individual phenotype and interact with other environmental factors such as temperature and drought. We used standardized growth rates of 105 Scots pine Pinus sylvestris located near Chernobyl, Ukraine, varying in the level of background radiation by almost a factor 700. Mean growth rate was severely depressed and more variable in 1987–1989 and several other subsequent years, following the nuclear accident in April 1986 compared to the situation before 1986. The higher frequency of years with poor growth after 1986 was not caused by elevated temperature, drought or their interactions with background radiation. Elevated temperatures suppressed individual growth rates in particular years. Finally, the negative effects of radioactive contaminants were particularly pronounced in smaller trees. These findings suggest that radiation has suppressed growth rates of pines in Chernobyl, and that radiation interacts with other environmental factors and phenotypic traits of plants to influence their growth trajectories in complex ways.

Spermatozoa vary greatly in size and shape among species across the animal kingdom. Postcopulatory sexual selection is thought to be the major evolutionary force driving this diversity. In contrast, less is known about how sperm size varies among populations of the same species. Here, we investigate geographic variation in sperm size in barn swallows Hirundo rustica, a socially monogamous passerine with a wide Holarctic breeding distribution. We included samples from seven populations and three subspecies: five populations of ssp. rustica in Europe (Czech, Italy, Norway, Spain, and Ukraine), one population of ssp. transitiva in Israel, and one population of ssp. erythrogaster in Canada. All sperm traits (head length, midpiece length, tail length, and total length) varied significantly among populations. The variation among the European rustica populations was much lower than the differences among subspecies, indicating that sperm traits reflect phylogenetic distance. We also performed a test of the relationship between the coefficient of between-male variation in total sperm length and extrapair paternity levels across different populations within a species. Recent studies have found a strong negative relationship between sperm size variation and extrapair paternity among species. Here, we show a similar negative relationship among six barn swallow populations, which suggests that the variance in male sperm length in a population is shaped by the strength of stabilizing postcopulatory sexual selection.

Females of several vertebrate species selectively mate with males on the basis of the major histocompatibility complex (MHC) genes. As androgen-mediated maternal effects have long-lasting consequences for the adult phenotype, both mating and reproductive success may depend on the combined effect of MHC genotype and exposure to androgens during early ontogeny. We studied how MHC-based mate choice in ring-necked pheasants (Phasianus colchicus) was influenced by an experimental in ovo testosterone (T) increase. There was no conclusive evidence of in ovo T treatment differentially affecting mate choice in relation to MHC genotype. However, females avoided mating with males with a wholly different MHC genotype compared with males sharing at least one MHC allele. Females also tended to avoid mating with MHC-identical males, though not significantly so. These findings suggest that female pheasants preferred males with intermediate MHC dissimilarity. Male MHC heterozygosity or diversity did not predict the expression of ornaments or male dominance rank. Thus, MHC-based mating preferences in the ring-necked pheasant do not seem to be mediated by ornaments’ expression and may have evolved mainly to reduce the costs of high heterozygosity at MHC loci for the progeny, such as increased risk of autoimmune diseases or disruption of coadapted gene pools.

Mutagenic and epigenetic effects of environmental stressors and their transgenerational consequences are of interest to evolutionary biologists because they can amplify natural genetic variation. We studied the effect of parental exposure to radioactive contamination on offspring development in lesser marsh grasshopper Chorthippus albomarginatus. We used a geometric morphometric approach to measure fluctuating asymmetry (FA), wing shape and wing size. We measured time to sexual maturity to check whether parental exposure to radiation influenced offspring developmental trajectory and tested effects of radiation on hatching success and parental fecundity. Wings were larger in early maturing individuals born to parents from high radiation sites compared to early maturing individuals from low radiation sites. As time to sexual maturity increased, wing size decreased but more sharply in individuals from high radiation sites. Radiation exposure did not significantly affect FA or shape in wings nor did it significantly affect hatching success and fecundity. Overall, parental radiation exposure can adversely affect offspring development and fitness depending on developmental trajectories although the cause of this effect remains unclear. We suggest more direct measures of fitness and the inclusion of replication in future studies to help further our understanding of the relationship between developmental instability, fitness and environmental stress.

Sperm are highly susceptible to reactive oxygen species (ROS) that can damage sperm DNA and structure, resulting in reduced fertilizing capacity. Exposure to radioactive contamination can also impair sperm swimming behavior and fertilizing ability, both through a reduction of sperm DNA integrity and via an increased generation of reactive oxygen species (ROS). However, the relationship between individual oxidative status and sperm swimming behavior has never been investigated in any wild population of animals exposed to radioactive contamination. We studied the motility of sperm collected from barn swallows, Hirundo rustica, breeding under different levels of radioactive contamination following the Chernobyl accident in 1986, in relation to individual oxidative status. We tested the hypothesis that the degree of impairment of sperm swimming behavior by radioactive contamination depended on plasma antioxidant capacity, the level of reactive oxygen metabolites (ROMs) and oxidative stress (sensu Costantini et al. 2006), a better oxidative status being associated with higher sperm motility. Sperm behavior parameters were subjected to principal component (PC) analysis, which extracted four PCs explaining 86% of the variance in sperm motility. PC2, representing sperm with high track velocity and ample lateral head displacement, was significantly predicted by the interaction between radiation level and either oxidative damage or oxidative stress. Contrary to our predictions, the highest values of PC2 were associated with relatively high radiation levels, particularly for high levels of either ROMs or oxidative stress. In addition, there was a tendency for values of PC3 (representing the percent of motile sperm) and PC4 (representing slow sperm with high beat cross frequency) to depend on the interaction between radiation level and total plasma antioxidant protection. Our results confirm the importance of oxidative status in determining the genetic and physiological outcome of exposure to radioactive contamination, complementing previous studies relating sperm abnormality to circulating levels of specific antioxidants. Our results also complement previous evidence that oxidative damage of sperm was negatively related to sperm motility, thus indicating a possible trade-off in quenching pro-oxidant compounds in the plasma and the seminal fluid.

Maternal effects through albumen quality are largely unexplored, despite the fundamental role that albumen exerts as source of proteins and water, as well as for antimicrobial defence of the embryo. We analysed the variation of two major albumen antimicrobials, avidin and lysozyme, by extracting samples from freshly laid eggs of the yellow-legged gull (Larus michahellis) and by correlating their levels to egg features. Lysozyme concentration increased along the laying sequence, while avidin concentration decreased. Both antimicrobials declined during the season. In addition, avidin concentration declined from first- to last-laid male eggs, whereas the opposite was true among the female eggs. We also analysed chick body mass and size and immune response, in relation to albumen antimicrobial levels in their original egg while controlling for potential covariation between egg quality and rearing conditions by cross-fostering eggs between nests. Tarsus length decreased with avidin concentration, particularly early in the season. Avidin concentration negatively predicted tarsus length of chicks and the phytohaemagglutinin response of females, but not males. However, chick phenotype did not covary with lysozyme albumen concentration. This is the first study where maternal effects mediated by albumen antimicrobials are investigated in relation to both sex and egg features in any wild bird species. Whether the observed patterns of variation in antimicrobial concentration are the by-product of maternal physiological constraints, or reflect adaptive allocation strategies, cannot be ascertained. The covariation between chick cell-mediated immunity and albumen avidin concentration might be causal, according to the documented effects of albumen proteins on immunity in other species.

The Chernobyl nuclear accident produced the largest unintended release of radionuclides in history, with dramatic consequences for humans and other organisms. Exposure to ionizing radiation is known to reduce circulating and stored levels of specific antioxidants in birds and humans, thus potentially increasing oxidative stress. However, overall effects of radioactive exposure on oxidative status have never been investigated in any free ranging vertebrate. We measured plasma antioxidant capacity and concentration of reactive oxygen metabolites in adult barn swallows (Hirundo rustica) from colonies with variable background radiation levels in the Chernobyl region in Ukraine and Belarus. We predicted that antioxidants would decrease while reactive oxygen metabolites would increase with exposure to increasing levels of radiation at the breeding sites. Consistent with this expectation, radiation level positively predicted plasma concentration of reactive oxygen metabolites, whereas no significant covariation was found with non-enzymatic plasma antioxidant capacity. An index of oxidative stress was also larger in barn swallows exposed to high contamination levels. Thus, radioactive contamination appeared to be responsible for the increased generation of reactive oxygen metabolites and the imbalance between reactive oxygen metabolites and non-enzymatic plasma antioxidant capacity.

In avian species, maternal provisioning to the eggs is predicted to be more valuable for the offspring under adverse environmental conditions and intense sibling competition. However, studies manipulating both the amount of maternal pre-hatching resources and the harshness of post-hatching environment have seldom been performed to date. In this experimental study of Barn Swallow (Hirundo rustica) nestlings, we tested the consequences of a reduction in the albumen content of the eggs for fitness-related offspring traits, while performing an unbalanced partial cross-fostering soon after hatching, either increasing or decreasing brood size by one nestling. By molecular sexing of the chicks, we additionally tested for sex-specific sensitivity of individual nestlings to experimental treatments and to sex ratio variation in nestmates. We predicted that chicks hatching from albumen-deprived eggs should suffer more than control chicks from the harsher rearing conditions of enlarged broods. However, although albumen removal depressed chick body mass, chicks hatching from control eggs did not fare better than those hatching from eggs with reduced albumen content in enlarged vs. reduced broods. Albumen removal had sex-specific effects on immunity, with males, but not females, hatching from eggs with reduced albumen content showing a lower T-cell-mediated immune response than controls, suggesting that the two sexes were differentially susceptible to resource deprivation during early ontogeny. In addition, both immune response and chick body mass at age 7 days, when maximum growth rate is attained, declined with an increasing proportion of male nestmates. The effect of brood size manipulation on chick body mass at age 12 days, when peak body mass is attained, was also found to depend on brood sex composition, in that an increase in the proportion of male nestmates depressed offspring body mass in reduced broods, while the reverse was true in enlarged broods. On the whole, these findings suggest that sex differences may exist in environmental sensitivity and patterns of resource allocation among different body functions, and that brood size variation and sex composition may affect offspring fitness-related traits.

Summary 1Egg size is an important maternal trait that can have major consequences on offspring phenotype. However, the effects of the variation of different components of cleidoic eggs have been little investigated. 2Here, we addressed whether a reduction of the relative egg albumen content within the natural range of variation affects viability, time to hatching, early post-natal begging displays, morphology and immune response of yellow-legged gull Larus michahellis chicks. 3Egg mass strongly positively predicted chick size and mass at all ages, while time to hatching positively predicted tarsus length and immune response, irrespective of albumen removal. Variation in time to hatching may thus affect immune system maturation. 4Albumen removal resulted in a lower embryonic viability and increased time to hatching of individual eggs. The probability that an egg originated a chick surviving until 8 days of age increased with original egg mass among controls, but not among chicks hatching from eggs with reduced albumen content (‘albumen chicks’). 5Begging rate increased with laying order among albumen chicks while it decreased among controls. Concomitantly, begging rate decreased with egg mass among controls while it did not vary among albumen chicks. Surprisingly, albumen removal did not affect body mass or tarsus length except at 8 days of age, when control chicks were lighter than albumen chicks. 6In conclusion, our study indicates that a reduction of the relative egg albumen content can have complex effects on offspring development, behaviour and viability of a semiprecocial bird, suggesting that the relative albumen content of the eggs represents an important mechanism of maternal effects.

A number of studies have assessed or modeled the distribution of the radionuclides released by the accident at the Fukushima-Daiichi Nuclear Power Plant (FDNPP). Few studies however have investigated its consequences for the local biota. We tested whether exposure of barn swallow (Hirundo rustica) nestlings to low dose ionizing radiation increased genetic damage to their peripheral erythrocytes. We estimated external radiation exposure by using thermoluminescent dosimeters and by measuring radioactivity of the nest material. We then assessed DNA damage by means of the neutral comet assay. In addition, we conducted standard point-count censuses of barn swallows across environmental radiation levels and estimated their abundance and local age ratio. Radioactivity of nest samples was in the range 479–143,349 Bq kg−1, while external exposure varied between 0.15 and 4.9 mGy. Exposure to radioactive contamination did not correlate with higher genetic damage in nestlings. However, at higher levels of radioactive contamination the number of barn swallows declined and the fraction of juveniles decreased, indicating lower survival and lower reproduction and/or fledging rate. Thus, genetic damage to nestlings does not explain the decline of barn swallows in contaminated areas and a proximate mechanism for the demographic effects documented here remains to be clarified.

The meltdown of the Chernobyl Nuclear Power Plant in 1986 resulted in numerous deleterious ecological effects on the area's wildlife. Currently, a 30-km radius area around the disaster site (known ...

In humans, most of the mammals and one bird species studied so far, the relative length of individual digits is sexually dimorphic. Most studies of humans have been concerned with the ratio between second (2D) and fourth digits (4D), whereas some studies of humans and other mammals have also investigated other digit ratios. Inter- and intra-sexual variation in 2D:4D may depend on differential exposure to androgens during embryonic life, and the genetic mechanisms linking 2D:4D to androgens may be mediated by Hox genes. Because Hox genes are conserved in vertebrates, similar patterns of variation in digit ratios might be expected across vertebrate classes. The observation of correlations between digit ratios and physiological, psychological and performance traits in humans has generated interest in exploring the possibility that digit ratios are a marker of embryonic exposure to androgens, which have diverse consequences on several phenotypic traits. However, the hypothesis that digit ratios depend on androgen effects during development has never been tested experimentally. In this study, we increased testosterone concentration in ring-necked pheasant eggs and measured length ratios between the second, third and fourth digits of both feet in fully grown offspring. Females from testosterone-injected eggs had larger 2D:3D in the left foot, whereas this was not the case in males. The other digit ratios were unaffected by hormone treatment in both sexes. However, digit ratios showed no sexual dimorphism among controls. Thus, present results are consistent with the hypothesis that variation in testosterone levels during development affects digit ratios.

Females of several vertebrate species selectively mate with males on the basis of the major histocompatibility complex (MHC) genes. As androgen-mediated maternal effects have long-lasting consequences for the adult phenotype, both mating and reproductive success may depend on the combined effect of MHC genotype and exposure to androgens during early ontogeny. We studied how MHC-based mate choice in ring-necked pheasants (Phasianus colchicus) was influenced by an experimental in ovo testosterone (T) increase. There was no conclusive evidence of in ovo T treatment differentially affecting mate choice in relation to MHC genotype. However, females avoided mating with males with a wholly different MHC genotype compared with males sharing at least one MHC allele. Females also tended to avoid mating with MHC-identical males, though not significantly so. These findings suggest that female pheasants preferred males with intermediate MHC dissimilarity. Male MHC heterozygosity or diversity did not predict the expression of ornaments or male dominance rank. Thus, MHC-based mating preferences in the ring-necked pheasant do not seem to be mediated by ornaments' expression and may have evolved mainly to reduce the costs of high heterozygosity at MHC loci for the progeny, such as increased risk of autoimmune diseases or disruption of coadapted gene pools.

Phenological responses to climate change vary among taxa and across trophic levels. This can lead to a mismatch between the life cycles of ecologically interrelated populations (e.g. predators and prey), with negative consequences for population dynamics of some of the interacting species. Here we provide, to our knowledge, the first evidence that climate change might disrupt the association between the life cycles of the common cuckoo ( Cuculus canorus ), a migratory brood parasitic bird, and its hosts. We investigated changes in timing of spring arrival of the cuckoo and its hosts throughout Europe over six decades, and found that short-distance, but not long-distance, migratory hosts have advanced their arrival more than the cuckoo. Hence, cuckoos may keep track of phenological changes of long-distance, but not short-distance migrant hosts, with potential consequences for breeding of both cuckoo and hosts. The mismatch to some of the important hosts may contribute to the decline of cuckoo populations and explain some of the observed local changes in parasitism rates of migratory hosts.

Carbon isotopic evidence revealed Deepwater Horizon (DWH) oil entering coastal planktonic and lower terrestrial food webs. The integration of spilled oil into higher terrestrial trophic levels, however, remains uncertain. We measured radiocarbon (14C) and stable carbon (13C) in seaside sparrow (Ammodramus maritimus) feathers and crop contents. Lower 14C and 13C values in feathers and crop contents of birds from contaminated areas indicated incorporation of carbon from oil. Our results, although based on a small sample of birds, thus reveal a food-web link between oil exposure and a terrestrial ecosystem. They also suggest that the reduction in reproductive success previously documented in the same population might be due to the (direct) toxic effect of oil exposure, rather than to (indirect) ecological effects. We recommend future studies test our results by using larger samples of birds from a wider area in order to assess the extent and implications of DWH oil incorporation into the terrestrial food web.

Success in competition for limiting parental resources depends on the interplay between parental decisions over allocation of care and offspring traits. Birth order, individual sex and sex of competing siblings are major candidates as determinants of success in sib–sib competition, but experimental studies focusing on the combined effect of these factors on parent–offspring communication and within-brood competitive dynamics are rare. Here, we assessed individual food intake and body mass gain during feeding trials in barn swallow chicks differing for seniority and sex, and compared the intensity of their acoustic and postural solicitation (begging) displays. Begging intensity and success in competition depended on seniority in combination with individual sex and sex of the opponent. Junior chicks begged more than seniors, independently of satiation level (which was also experimentally manipulated), and obtained greater access to food. Females were generally weaker competitors than males. Individual sex and sex of the opponent also affected duration of begging bouts. Present results thus show that competition with siblings can make the rearing environment variably harsh for developing chicks, depending on individual sex, sex of competing broodmates and age ranking within the nest. They also suggest that parental decisions on the allocation of care and response of kin to signalling siblings may further contribute to the outcome of sibling competition.

We investigated levels of DNA damage in blood cells of barn swallows (Hirundo rustica) inhabiting the Chernobyl region to evaluate whether chronic exposure to low-level radioactive contamination continues to induce genetic damage in free-living populations of animals. Blood samples were obtained from barn swallows collected at sites with different background levels of radiation, including a relatively uncontaminated area. The extent of DNA damage was evaluated using the alkaline (pH = 12.1) comet assay, a robust and sensitive electrophoresis-based technique widely employed in research ranging from biomonitoring to clinical studies. We found that levels of DNA damage, as indexed by the extent of DNA migration, were increased in barn swallows living in areas surrounding Chernobyl when compared to swallows sampled at low-level sites. The results we obtained are consistent with previous findings on this same species, which showed that swallows breeding in areas heavily contaminated with radionuclides have increased mutation rates, higher oxidative stress and incidence of morphological aberrations and tumors. Overall, these results indicate that chronic exposure to radioactive contaminants, even 20 years after the accident at the Chernobyl nuclear power plant, continues to induce DNA damage in cells of free-living animals.

Carotenoids perform important biological actions in animal tissues, including contributing antioxidant protection. However, the function of transmission of maternal carotenoids to bird eggs is still largely unknown. We made a yolk biopsy of yellow-legged gull (Larus michahellis) eggs and found that the concentration of lutein declined with laying date and across the laying order and increased with egg mass. The concentration of all the main carotenoids (lutein, zeaxanthin, and dehydrolutein) pooled also declined with date and increased with egg mass. We also performed a partial reciprocal cross-fostering of eggs between clutches and investigated the covariation between morphology, T cell-mediated immunity, and plasma carotenoid concentrations of the chicks and carotenoid concentrations in their original eggs. Absolute plasma carotenoid concentrations did not covary with those in the yolk, whereas a positive covariation was found for relative concentrations. Yolk and absolute plasma carotenoid concentrations positively predicted chick body mass and size but not the intensity of the cell-mediated immune response. Thus, yolk carotenoid concentrations may affect chick carotenoid profile and growth, possibly mediating early maternal effects. However, rearing conditions also contributed to determining relative concentrations of circulating carotenoids. Since yolk or plasma antioxidant capacity did not correlate with carotenoid concentrations, future studies of maternal effects mediated by antioxidants should integrate information on carotenoids with information on other components of the antioxidant systems.

Maternal effects mediated by egg quality are important sources of offspring phenotypic variation and can influence the course of evolutionary processes. Mothers allocate to the eggs diverse antioxidants that protect the embryo from oxidative stress. In the yellow-legged gull (Larus michahellis), yolk antioxidant capacity varied markedly among clutches and declined considerably with egg laying date. Analysis of bioptic yolk samples from clutches that were subsequently partially cross-fostered revealed a positive effect of yolk antioxidant capacity on embryonic development and chick growth, but not on immunity and begging behaviour, while controlling for parentage and common environment effects. Chick plasma antioxidant capacity varied according to rearing environment, after statistically partitioning out maternal influences mediated by egg quality. Thus, the results of this study indicate that egg antioxidants are important mediators of maternal effects also in wild bird populations, especially during the critical early post-hatching phase.

BackgroundRadiation has negative effects on survival of animals including humans, although the generality of this claim is poorly documented under low-dose field conditions. Because females may suffer disproportionately from the effects of radiation on survival due to differences in sex roles during reproduction, radiation-induced mortality may result in male-skewed adult sex ratios.Methodology/principal findingWe estimated the effects of low-dose radiation on adult survival rates in birds by determining age ratios of adults captured in mist nets during the breeding season in relation to background radiation levels around Chernobyl and in nearby uncontaminated control areas. Age ratios were skewed towards yearlings, especially in the most contaminated areas, implying that adult survival rates were reduced in contaminated areas, and that populations in such areas could only be maintained through immigration from nearby uncontaminated areas. Differential mortality in females resulted in a strongly male-skewed sex ratio in the most contaminated areas. In addition, males sang disproportionately commonly in the most contaminated areas where the sex ratio was male skewed presumably because males had difficulty finding and acquiring mates when females were rare. The results were not caused by permanent emigration by females from the most contaminated areas because none of the recaptured birds had changed breeding site, and the proportion of individuals with morphological abnormalities did not differ significantly between the sexes for areas with normal and higher levels of contamination.Conclusions/significanceThese findings are consistent with the hypothesis that the adult survival rate of female birds is particularly susceptible to the effects of low-dose radiation, resulting in male skewed sex ratios at high levels of radiation. Such skewed age ratios towards yearlings in contaminated areas are consistent with the hypothesis that an area exceeding 30,000 km(2) in Chernobyl's surroundings constitutes an ecological trap that causes dramatic excess mortality.

Background Animals living in areas contaminated by radioactive material from Chernobyl suffer from increased oxidative stress and low levels of antioxidants. Therefore, normal development of the nervous system is jeopardized as reflected by high frequencies of developmental errors, reduced brain size and impaired cognitive abilities in humans. Alternatively, associations between psychological effects and radiation have been attributed to post-traumatic stress in humans. Methodology/Principal Finding Here we used an extensive sample of 550 birds belonging to 48 species to test the prediction that even in the absence of post-traumatic stress, there is a negative association between relative brain size and level of background radiation. We found a negative association between brain size as reflected by external head volume and level of background radiation, independent of structural body size and body mass. The observed reduction in brain size in relation to background radiation amounted to 5% across the range of almost a factor 5,000 in radiation level. Species differed significantly in reduction in brain size with increasing background radiation, and brain size was the only morphological character that showed a negative relationship with radiation. Brain size was significantly smaller in yearlings than in older individuals. Conclusions/Significance Low dose radiation can have significant effects on normal brain development as reflected by brain size and therefore potentially cognitive ability. The fact that brain size was smaller in yearlings than in older individuals implies that there was significant directional selection on brain size with individuals with larger brains experiencing a viability advantage.

Genotoxic chemicals, through damage and alteration of the genetic material of wild organisms, pose significant threats to the persistence of wild animal populations. Their damaging effects can ultimately impair the health of the ecosystem and its provision of services to human society. Bird species are good candidates for the role of sentinels of the effects of genotox-ins, thanks to (i) the diversity of their ecological niches, (ii) their ubiquity across environments, (iii) their conspicuousness, abundance and approachability, together with (iv) their well-known life histories and the availability of historical data series. Avian diversity increases the likelihood that adequate model species be available for monitoring genotoxicants and assessing their impact. This paper reviews the methods utilized by genetic ecotoxicological studies of wild birds, highlighting their benefits and shortcomings. It also summarizes the genetic ecotoxicological studies so far conducted. In spite of a paucity of studies, several classes of genotoxicants have already been investigated across a variety of species and environments, thus supporting the versatility of birds as monitors of genotoxic contamination. Future technical advancements and applications are suggested, with particular reference to the analysis of mutational events, gene expression and methylation patterns. Finally, I argue that the development of avian genetic ecotoxicology will contribute to the understanding of natural variation in the underlying machinery for coping with DNA damage and oxidative stress, both of which are increasingly recognized as proximate factors in the evolution of life history adaptations.